A deformable mirror device is similar to a small mirror which may rotate with respect to a fixed axis. Deformable mirror devices are widely utilized in reflection type display devices. The use of a deformable mirror device is illustrated in FIG. 1 which refers to U.S. Pat. No. 5,287,096.
As seen in FIG. 1 a reflecting surface 10 may rotate about a fixed axis. The degree of rotation of the reflecting surface 10 is illustrated by the dashed lines of FIG. 1. Light incident upon the reflecting surface 10 is reflected based upon whether the reflecting surface 10 is tilted. The reflected light from the reflecting surface 10 is then focused on a screen to form a portion of an image.
A complete image is formed by selectively tilting a number of reflecting surfaces such that each reflecting surface corresponds to a different portion of an image. Each reflecting surface, therefore, corresponds to a "picture element" or "pixel" and the pixels combine to create an image. The pixels are then repeatedly scanned at a "refresh rate" to provide the impression that the pixels create an image. The amount of time between refresh of a pixel is called the refresh time.
By varying the percentage of the refresh time that the reflecting surfaces are tilted the intensity of the light focused on the screen may be varied to create an image. Thus, for example, if a reflecting surface is tilted for the entire refresh time then the maximum intensity of light is focused on the screen to create the brightest portion of the screen. If, however, the reflecting surface is only tilted for 50% of the refresh time, then less light intensity is focused on the screen because light is only focused on the screen for half the time of the previous example. The intensity of light, and, therefore, the brightness of a portion of the screen, may in such a manner be controlled by controlling the duration which the reflecting surface is tilted.
In a conventional system, to adjust the brightness of portions of the screen to provide an image an analog image signal is digitally processed. This digital processing is conventionally carried out utilizing a static random access memory (SRAM) which is formed on a substrate under a reflection plate. The digital technology then adjusts the time that the SRAM cell is in the "1" state. The time that the SRAM cell is in the "1" state is adjusted by providing a digital value where the most significant bit of the digital value corresponds to 1/2 the refresh time of the display and where the least significant bit of the digital value corresponds to 1/2.sup.n of the refresh time, where n is the number of bits in the digital value. Thus, the time that the SRAM is in the "1" state is controlled by dividing the total refresh time into n steps. This necessitates in each SRAM cell of the display being capable of being updated to go from the "0" state to the "1" state and back to the "0" state in 1/2.sup.n of the refresh time.
Unfortunately, as the number of levels of brightness increases the speed with which the SRAM must change states also increases. Thus, for example, with an 8 bit value which results in a 256 level gray scale, the display device should be capable of changing the state of each SRAM cell in the entire array of cells twice within 65 microseconds. As the number of pixels in the display increases, the ability to revise the SRAM cell states within the necessary time becomes more difficult. Furthermore, as the number of grey scales increases the problem of changing states of all of the cells in the display becomes even more problematic as the devices must be capable of two changes of state within 1/2.sup.n of the refresh time.
In addition to the requirements of high speed SRAM to control the reflecting plates, a display device utilizing the conventional digital technology typically incorporates devices to digitally process the analog image signal. These devices may be numerous and may also suffer from having to meet the same performance levels as the SRAM cells which control the reflecting surfaces.
In light of the above discussion, there exists a need for improvements in reflection type display devices.